verprovisioning is widely used by packet network engineering teams to protect networks against network element failure and support the rapid growth of traffic volume. So far, this approach has been successful in maintaining simple, scalable, highly available, and robust networks. It is important to realize that in packet networks which do not perform call admission control, there is often no way to control the amount or types of traffic entering the network. The provisioning problem therefore lies in figuring out how much excess capacity is required to provide robustness (e.g., resilience to multiple simultaneous link failures) and scalability. The current tools for network management, such as Simple Network Management Protocol (SNMP), are limited in their capabilities, since they only provide highly aggregated statistics about the traffic (e.g., average traffic load over fiveminute intervals) and do not give insight into traffic dynamics on timescales appropriate for events such as packet drops. Another example is the demand traffic matrix, which is a crucial input to many network planning, provisioning, and engineering problems, but is difficult to obtain with available tools [1,2].Detailed traffic measurements are necessary to assess the capacity requirements and efficiently engineer the network. In this article we first describe the architecture and capabilities of the IPMON system. Then we point out the challenges we faced in collecting terabytes of data, and include our solutions to data sanitization. In the remainder of the article we AbstractNetwork traffic measurements provide essential data for networking research and network management. In this article we describe a passive monitoring system designed to capture GPS synchronized packet-level traffic measurements on OC-3, OC-12, and OC-48 links. Our system is deployed in four POPs in the Sprint IP backbone. Measurement data is stored on a 10 Tbyte storage area network and analyzed on a computing cluster. We present a set of results to both demonstrate the strength of the system and identify recent changes in Internet traffic characteristics. The results include traffic workload, analyses of TCP flow round-trip times, out-of-sequence packet rates, and packet delay. We also show that some links no longer carry Web traffic as their dominant component to the benefit of file sharing and media streaming. On most links we monitored, TCP flows exhibit low out-of-sequence packet rates, and backbone delays are dominated by the speed of light.

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